The present application relates to a system for distributing messages to pagers, and more particularly to a system for distributing messages to pagers in a multi-channel system where not all channels may be used simultaneously with all other channels.
Typical paging systems operate using a synchronized set of omnidirectional (or wide sector) transmitters distributed over a service area. Each omnidirectional transmitter simultaneously broadcasts (simulcasts) to all the pagers in a region surrounding it. Although, each pager located in the region may receive each broadcast, some messages may be addressed to a particular pager and only this pager will listen or take action in response to the received message. Some protocols such as FLEX from Motorola of Schaumburg, Ill. specify that pagers only wake up at certain intervals and the pager transmitter must take into account the wake up time of a particular pager when deciding the time to direct a message to it.
Multi-channel approaches to operating a pager transmitter are however also possible. Co-assigned U.S. patent application Ser. No. 08/808,347 discloses a paging system that replaces the prior art omnidirectional approach with a multi-beam transmission scheme wherein a single transmission site transmits over multiple beams on a single frequency with the beams being isolated from one another so that different beams may simultaneously carry different signals over the same frequency. This approach greatly increases the amount of message traffic that can be accommodated using a single transmitter site on a single frequency.
However, one can see that the task of scheduling and controlling the transmission of a message addressed to a particular pager is now much more complicated since not only the transmission time must be selected but the correct beam must also be selected. The task is further complicated by antenna design constraints which prevent certain beams from being used simultaneously with certain other beams to carry different signals.